1. Field of the Invention
The invention relates generally to biomass fuels derived from plant sources. In particular aspects, the invention relates to a terpenoid-based fuel produced by a cracking/reduction process or by irradiation. The process may be controlled to produce a biomass fuel having variable percentages of benzenoid compounds useful, for example, as per se fuels, as fuel additives or as octane enhancers for conventional gasoline fuels.
2. Description of the Related Art
Increasing attention is being focused on problems associated with diminishing supplies of fossil fuels. These problems center on economic and ecologic considerations. It is recognized that oil and gas sources are exhaustible and that world politics may seriously jeopardize attempts to manage presently identified petroleum reserves. These are strong economic factors having potential effects on many facets of business and quality of life. There is also increasing concern over the pollution generated by fossil fuel burning which causes extensive and perhaps irreversible ecological harm. Consequently, fuel performance is becoming more of a concern, since highly efficient fuels, especially for internal combustion engines, will decrease or eliminate toxic emissions and cut operation costs.
Approaches to these problems have included efforts to develop total substitutes or compatible blends for petroleum-based fuels. For example, engines will operate efficiently on natural gas or alcohol. However, this requires engine modifications that are relatively expensive and at the present considered impractical in view of present production and sheer numbers of extant engines. With pure methanol, corrosion, particularly evident in upper-cylinder wear may be a problem (Schwartz, 1986).
Biomass sources have been explored as fuel source alternatives to petroleum. Biomass is defined as organic matter obtained from agriculture or agriculture products. Many side-products of foods, for example, are inefficiently used, leading to large amounts of organic waste. Use of such waste as a fuel per se or as a blend compatible with existing petroleum based fuels could extend limited petroleum reserves, reduce organic waste and, depending on the processing of the organic waste, provide a less expensive alternate fuel or fuel blends.
One of the more common components of plants and seeds is a group of alicyclic hydrocarbons classified as terpenes. Pinene and limonene are typical examples of monocyclic terpenes. Both have been tested as fuels or fuel additives. The Whitaker reference (1922) discloses the use of a terpene, as a blending agent for alcohol and gasoline or kerosene mixtures. A fuel containing up to about 15% of steam distilled pine oil was claimed to be useful as a motor fuel. Nevertheless, pinene was useful mainly to promote soluble mixtures of ethyl alcohol, kerosene and gasoline. There were no disclosed effects on fuel properties nor was there disclosed any further processing of the pinene.
Two United States patents describe a process for purifying limonene for use as a fuel or fuel additive (Whitworth, 1989, 1990). The process includes distillation of limonene-containing oil followed by removal of water. The distilled limonene, blended with an oxidation inhibitor such as p-phenylenediamine, is claimed as a gasoline extender when added in amounts up to 20% volume. Unfortunately, in actual testing under a power load in a dynamometer, addition of 20% limonene to unleaded 87 octane gasoline results in serious preignition, casting serious questions as to its practical value as a gasoline extender.
On the other hand, Zuidema (1946) discloses the use of alicyclic olefins such as limonene, cyclohexene, cyclopentene and menthenes without modification as stabilization additives for gasoline. These compounds contain at least one double bond, a characteristic that apparently contributes to the antioxidant effect of adding these compounds to gasolines in amounts not exceeding 10% by volume.
U.S. Pat. No. 4,300,009 (Haag, 1981) is concerned with the conversion of biological materials to liquid fuels. Although relating in major part to zeolite catalytic conversion of plant hydrocarbons having weights over 150, a limonene/water feed was shown to produce about 19% toluene when pumped over a fixed bed zeolite catalyst at 482.degree. C. at atmospheric pressure. Unfortunately, monocyclic aromatic compounds were reported to comprise only about 40% of the total products, of which major components were toluene and ethylbenzene. A disadvantage with the use of zeolite catalyst was the need to fractionate the aromatic compounds from the product mixture to obtain gasoline or products useful as chemicals. Formation of undesirable coke was also disclosed as a potential problem, in view of its tendency to inactivate zeolite catalysts.
Biomass fuel extenders such as methyltetrahydrofuran (MTHF) have been tested as alternative fuels (Rudolph and Thomas, 1988), but appear to be relatively expensive as pure fuels. As an additive in amounts up to about 10%, MTHF compares favorably with tetraethyl lead.
Fuel mixtures suitable as gasoline substitutes have also been prepared by mixing various components, for example C.sub.2 -C.sub.7 hydrocarbons, C.sub.4 -C.sub.12 hydrocarbons and toluene (Wilson, 1991). Toluene, and other substituted monocyclic benzenoid compounds such as 1,3,5-trimethylbenzene, 1,2,3,4-tetramethylbenzene, o-, m- and p-xylenes, are particularly desirable as octane enhancers in gasolines and may be used to supplement gasolines in fairly large percentages, at least up to 40 or 50 percent.
Generally, processes for obtaining aromatic compounds are synthetic procedures. Therefore it is relatively expensive to use aromatic liquid hydrocarbons as fuels or blends for gasoline fuels. On the other hand, a biomass source of easily isolated aromatic compounds would be less expensive, provide an efficient disposal of organic waste, and conserve petroleum reserves by extending or possibly replacing gasoline fuels. Although aromatic hydrocarbons occur naturally and are isolable from plant sources, it is impractical to isolate these compounds from biomass material because of the relatively low amounts present.